266 



AGRICULTURAL INDICATORS. 



duction may ultimately be forecasted with something of the accuracy of daily 

 weather forecasts at present. 



The excess-deficit balance. — The fact has already been emphasized that an 

 excess of rainfall in one year is almost certain to be balanced by a deficit in 

 the next year, while a great excess is often followed by two or rarely three 

 years of deficit. As a rule, an excess is an amount above the normal rainfall 

 and a deficit is an amount below it. Moreover, an excess in one region is often 

 counterbalanced by a deficit in another, or an increase or decrease in one 

 region is not met by a corresponding change in an adjacent one. When the 

 balance operates from one year to another, it produces a cycle of 2 to 3 years. 

 This cycle exhibits marked variations in rainfall, so much so that it may 

 obscure the normal effect of the 11-year cycle at its maximum or minimum, 

 though apparently not that of the 22-year cycle. In order to illustrate the 

 operation of the excess-deficit cycle, use has been made of columnar graphs of 

 the rainfall at widely separated points in the grassland climax. The points 

 selected are Williston (North Dakota), Cheyenne (Wyoming), Akron (Colo- 

 rado), and Amarillo (Texas). In the case of the first three places, the graphs 

 have been adapted from those prepared respectively by Babcock (1915:5,) 

 Jones (1916:4), and McMurdo (1916:4). The graph of Williston rainfall 



10 



Mflll l I M 







1900 1905 1910 1915 



Fig. 18. — Graph of total and seasonal rainfall at Akron, Colorado. 



